A trial of exemestane with or without everolimus for breast cancer that is oestrogen receptor positive and has spread outside the breast (BOLERO 2)

Cancer type:

Breast cancer




Phase 3

This trial was looking at exemestane and everolimus (Afinitor) for breast cancer that is sensitive to the female hormone oestrogen (oestrogen receptor positive breast cancer). It recruited people with breast cancer that was locally advanced, or had spread to another part of the body (metastatic or secondary breast cancer).

Doctors often use hormone therapy to treat hormone receptor positive breast cancer. Letrozole and anastrozole are 2 hormone therapy drugs they commonly use. But if cancer comes back or continues to grow after having these drugs, doctors are not sure of the best treatment to use. In this trial, everybody had a hormone therapy drug called exemestane. Some people also had a drug called everolimus.

Everolimus (also known as RAD001) is a type of biological therapy.  It is a cancer growth blocker. It works by targeting a protein called mTOR and stops some of the signals it sends that make cancer cells divide and grow.

The aim of this trial was to see if everolimus and exemestane together worked better than exemestane alone for hormone receptor positive breast cancer that had come back or continued to grow after treatment with letrozole or anastrozole.

Summary of results

The trial team found that on average, women who took exemestane and everolimus had a longer period of time without any sign of their cancer getting worse than women who had exemestane alone.

The trial recruited 724 post menopausal Open a glossary item women who had hormone receptor positive, advanced breast cancer. Their average age was 62. All of them had already had a hormone therapy drug called an aromatase inhibitor. Many of the women had also had other types of hormone therapy and chemotherapy.

The trial was randomised so neither the women taking part nor their doctors could decide which treatment they had. And they didn’t know which treatment they were having either. This is called a double blind trial Open a glossary item.

  • 485 women had exemestane and everolimus
  • 239 had exemestane and a dummy drug (placebo Open a glossary item)

Women in the everolimus group had more side effects such as sore mouth, a drop in the number of red blood cells (anaemia Open a glossary item), shortness of breath and tiredness (fatigue).

The trial team followed up the women for an average of 18 months. They found that the average length of time women had without any sign of their cancer getting worse was

  • Just under 8 months for women who had exemestane and everolimus
  • Just over 3 months for women who had exemestane and placebo

Doctors call this an improvement in progression free survival. The researchers don’t yet know if adding everolimus to exemestane will help women to live longer overall.

We have based this summary on information from the team who ran the trial. The information they sent us has been reviewed by independent specialists (peer reviewed Open a glossary item) and published in a medical journal. The figures we quote above were provided by the trial team. We have not analysed the data ourselves.

Recruitment start:

Recruitment end:

How to join a clinical trial

Please note: In order to join a trial you will need to discuss it with your doctor, unless otherwise specified.

Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

Chief Investigator

Professor Robert Coleman

Supported by

National Institute for Health Research Cancer Research Network (NCRN)

Questions about cancer? Contact our information nurses

Freephone 0808 800 4040

Last review date

CRUK internal database number:

Oracle 5194

Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

Harriet wanted to try new treatments

A picture of Harriet

“I was keen to go on a clinical trial. I wanted to try new cancer treatments and hopefully help future generations.”

Last reviewed:

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